The purpose of the study is: 1. Determine what happens to microorganisms in carious dentin sealed from the oral cavity with a fissure sealant; 2. to determine, by sealing pits and fissures of permanent first molars exhibiting clinical and radiographic signs of caries, the progress or lack thereof, over time intervals of up to two or more years; 3. and to evaluate the usefulness and compare the cost with traditional restorative procedures within an incremental child dental care program. The bacteriological phase of the study has been completed. The total via"le count of infected dentin has decreased with time as the sealant had been in place. Although the major reduction in viable count occured during the first two weeks there was a gradual reduction in total count thereafter. At the end of the two years there was approximately a 2,000 fold decrease in the number of cultivable microorganisms from the dentin of sealed teeth compared with that of the unsealed control teeth. To date approximately seventy-five children of an anticipated total of 200 who have met the study criteria have been included in the study. They have been examined, sealants have been applied to the occlusal surface of first permanent molars on one side of the mouth and all necessary restorative treatment has been completed.